The invention relates to a wireless communications system employing Multi-Element Antennas (MEAs) at both the transmitter and receiver.
The transmission capacity (ultimate bit rate) of a digital wireless communications system is based on a number of different parameters including (a) total radiated power at the transmitter, (b) the number of antenna elements at the transmitter and receiver, (c) noise power at the receiver, (d) characteristics of the propagation environment, (e) bandwidth, etc. For a wireless transmission sysem employing an appreciable number of antennas at both the transmitter and receiver and operating in a so-called Rayleigh fading environment even without coding, the bit rate could be very large, e.g., 36 bits per second per Hz with a reasonable Signal to Noise Ratio (SNR) of 18 dB. Heretofore, it was difficult for a communications system to exchange data at a fraction of such a rate. The main reason for this is that the prior art did not appreciate the problems that had to be solved in order to building a large bit rate system.
We have recognized that a wireless communications system that transmits at a substantial bit rate may be achieved, in accordance with an aspect of the invention, by decomposing an m-dimensional system into m-one dimensional systems (of possibly a different capacity) when the transfer (H matrix) characteristics of the wireless channel are unknown to the transmitter. More specifically and in accordance with the principles of the invention, a burst of signal vectors is formed from different data symbols and then transmitted by a transmitter via a Multi-Element Antenna Array. The transmitted vector symbols are received as signal vectors by a plurality of different antennas associated with a wireless receiver. The symbol components of the transmitted vector symbol have an (arbitrary) order and the receiver determines the best reordering of these transmitted components and then processes the received vector to determine the reordered transmitted symbol components. Such processing starts with the lowest (e.g., first) level of the reordered components, and for each such level, cancels out interfering contributions from lower levels, if any, and nulls out interfering contributions from higher levels, if any.
Such receiver processing includes, in accordance with one embodiment of the invention, compensating the weaker of the received transmitted signal components by first removing the interference from the stronger of the received transmitted components, and then processing the result to form the bit decisions.
These and other aspects of the invention may be appreciated from the following detailed description, accompanying drawings and claims.